# eli5: Why c remains the same at any frame of reference?

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eli5: Why c remains the same at any frame of reference?

In: Physics

we dont know why.

we just know that it does, which predicts other things should be specific ways. when we test those, those are also true.

but asking why is pointless, it is a fundimental property of the universe that “just is”

Because we have seen that it does.

Some things in science are not explained by being something that has to be true because something else is true. Some things are just true because we have looked a lot, in many places, and seen that they just *are* true.

The speed of light in vacuum, c, has been observed to be constant in all reference frames. *Because* we have seen that this is true, we had to adjust our equations so that c remains the same no matter what. That couldn’t be possible in a world that worked like Newton’s laws work.

We have seen, for example, that the orbit of Mercury is distorted because of relativity. We have seen that muons, which should decay too fast to reach the Earth’s surface, can still reach that surface because they are flying at close to light speed. To us, the particle experiences time dilation: what is only a tiny fraction of a second to the muon is plenty of time to reach the Earth. From the muon’s perspective, what happens is, the *Earth* is approaching *it* at the speed of light, and thus the distance between the muon and the Earth contracts, making it short enough to fly through at its speed.

Why is c constant? Because every time we check to see if it’s constant, it is.

velocity is distance over time. if velocity is constant for any frame of reference, then time becomes the variable.